1. Field of the Invention
The present invention generally relates to a light emitting diode (LED), and, in particular, to a wafer bonding type LED.
2. Description of the Related Art
Light emitting diodes (LEDs) have been employed in a wide variety of applications, including optical displays, traffic lights, data storage apparatuses, communication devices, illumination apparatuses, and medical treatment equipment. How to improve the yield rate of LEDs is an important issue in the manufacturing process of LEDs.
In United States Patent Publication No. 2005/0077544, an LED is disclosed. As shown in FIG. 1, a light emitting stack 13 of the LED is adhered to a substrate 10 through an adhesive layer 111. The LED further comprises a transparent conductive layer 121 disposed between the light emitting stack 13 and the adhesive layer 111. A portion of the transparent conductive layer 121 is exposed by an etching process, and an electrode 151 is formed on the exposed portion of the transparent conductive layer 121.
Regarding the above-mentioned manufacturing process of the LED, the material of the transparent conductive layer 121 is selected from indium tin oxide, cadmium tin oxide, and the like. The indium tin oxide is deposited on the surface of the light emitting stack by vapour deposition to form the transparent conductive layer 121. Next, a first reactive layer 101 is deposited, and then a reflection layer 141 is deposited on the substrate. A second reactive layer 102 is deposited on the reflection layer 141, and then the transparent conductive layer 121 disposed on the light emitting stack 13 is adhered to the second reactive layer 102 disposed on the substrate 10 through the adhesive layer 111. Thereafter, a portion of the light emitting stack is removed by an etching process to expose a first surface where the transparent conductive layer 121 contacts with the light emitting stack 13. The first surface is where the indium tin oxide is deposited. FIG. 2 is a picture of the first surface taken by SEM (scanning electron microscope). As shown in FIG. 2, the first surface is flat. FIG. 3 is a picture of the second surface where indium tin oxide contacts with the first reactive layer taken by SEM. As shown in FIG. 3, the second surface is rough. The first surface is where the electrode contacts. However, the first surface is flatter, and therefore the adhesion between the electrode and the first surface is not enough. The electrode is apt to peel off from the first surface, resulting a low yield rate of the LED.
Besides, the thickness between the electrode and the adhesive layer is not enough; therefore, the adhesive layer can be damaged due to the stress generated during the following wire bonding process. Thus, the yield rate of the LED is low.